The fabrication of containers with thin thermoplastic walls from thermoplastic synthetic resins such as polyethylene and vinyl polymers has found increasing acceptance in recent years. Such containers may be made by a blow-molding process in which a hollow thermoplastic parison is injected or extruded into a cavity which is expanded to form a blow mold. Fluid is introduced into the interior of the parison while the latter is still in a plastically deformable state to expand the parison into contact with the walls of the mold, thereby producing a receptacle of small wall thickness and complex or simple design as may be desired.
A problem with such containers is that they occupy as much space in an empty state as in filled condition and hence create difficulties with respect to transport and storage in the empty condition between manufacture and filling.
It has been proposed to shape these containers so that they can be stacked, but the same problem is nevertheless present since stacking depends on the head and bottom shapes of the vessels only and does not permit large numbers of them to occupy a substantially smaller volume than is occupied by the same number individually. In other words, the neck of the container may have a configuration complementary to a recess in the bottom so that either the empty or the filled containers can be stacked, but this does not permit a reduction of the storage volume for empty containers to any significant extent.